In a wireless communication system, resource allocation is necessary to perform communication between a Base Station (BS) and User Equipments (UEs) served by the BS. Due to the different multiplexing modes of resources of the wireless communication system, different mechanisms, or configurations, should be adopted to perform the resource allocation. Currently, there are two popular multiplexing modes of resources in the art, i.e. Time Division Duplex (TDD) mode and Frequency Division Duplex (FDD) mode. In the TDD mode, a single bandwidth is shared by the BS and the respective UE for both DL communication and UL communication therebetween, and the sharing is performed by allotting different periods of time for DL communication and UL communication respectively. Here, as known in the art, Downlink (DL) (or forward link) refers to the communication link from the BS to the UE, and Uplink (UL) (or reverse link) refers to the communication link from the UE to the BS. This communication link may be established through Single In Single Out (SISO), Multiple In Single Out (MISO) or a Multiple In Multiple Out (MIMO) system.
In a TDD system, such as a TD-LTE (Time Division-Long Term Evolution) system, seven different DL-UL (downlink and uplink) configurations 0 through 6 are defined and thereby asymmetric DL-UL allocations are supported. FIG. 1 illustrates the seven DL-UL configurations currently employed in the TD-LTE system, where D represents the DL subframe, U denotes the UL subframe, and S corresponds to the special subframe. As shown in FIG. 1, each of the seven configurations provides a specific DL-UL allocation different from the others, which enables flexible DL-UL reconfiguration according to traffic demands. For instance, in layered heterogeneous networks, it would be of great interest to deploy different DL-UL configurations in different cells. This is because in small-cell scenario, traffic patterns may vary from cell to cell. Even within one cell, obvious DL and UL traffic fluctuations could be observed from time to time.
However, in current TD-LTE system, all cells employ the same DL-UL configuration and only static or semi-static configuration is implemented. That is, the DL-UL configuration would be adjusted in months, or even years and kept the same among different cells, which may not match the instantaneous traffic condition when significant variations of downlink and uplink traffic are observed. For example, as shown in FIG. 2, all the neighboring cells have the same DL-UL configuration 5, and as stated above, the configuration will never be changed (i.e. static configuration) or will only be changed after months or even years (i.e. semi-static configuration).
Currently, 3GPP (3rd Generation Partnership Project) is discussing dynamic DL-UL reconfiguration methods triggered by traffic condition variations, in which the reconfiguration process can be conducted every milliseconds (ms) depending on the traffic condition about the DL and UL data to be transmitted. In particular, the BS calculates the ratio of data volumes to be transmitted in the DL and UL buffers every X ms (here, X is an integer larger than 0, and preferably may be 10 or 640), and then selects from the seven configurations one configuration that has DL-UL ratio closest to the calculated data volume ratio for transmissions of the next X ms.
Even so, such methods are still not effective enough to achieve the best overall system performance since, in addition to the data volumes to be transmitted, many other factors such as transmission capability may have great impact on the selection of appropriate configuration as well. These factors should be taken into account when adjusting the DL-UL configuration in order to achieve promising overall system performance.